regulator: da9210: addition of device tree support

Addition of device tree support for DA9210.
Two files are modified, the driver source file and the binding document.

Updates for the regulator source file include an .of_match_table entry and
node match checking in the probe() function for a compatible da9210 string.

Minor binding documentation changes have been made to the title and the
example.

Tested-by: Steve Twiss <stwiss.opensource@diasemi.com>
Signed-off-by: Steve Twiss <stwiss.opensource@diasemi.com>
Signed-off-by: Mark Brown <broonie@kernel.org>